Double aged copper base alloys



Patented Mar. 3, 1942 UNITED I STATES PATENT OFFICE 2,275,188 DOUBLE AGED COPPER BASE ALLOYS No Drawing. Application August 1, 1940, Serial No. 349,297

2 Claims. (01. 14841.2) I

The present invention relates to precipitation hardenable copper base alloys and more particularly to a process for-improving the properties of such alloys. In my copending application Serial No. 100,561, now Patent 2,225,339, December 17, 1940, and entitled "Precipitation hardened copper alloys, of which the present application is a continuation in part, there is disclosed a double aging process as applied to copper-chromium-beryllium alloys. I have found that the method disclosed in my prior application is applicable not only to copper-chromium v beryllium alloys but is in general applicable to all copper base precipitation hardenable alloys.

However, for convenience and brevity my inven- 15 tion will be described particularly as applied to copper-chromium-berryllium alloys. Alloys of,

this composition are disclosed in the patent to Dahl, 1,847,929, and generally contain about 0.1% to 1% berryllium, about 0.4% to 6% chromium with the remainder copper.

The alloy disclosed in the Dahl patent is age or precipitation hardened byheating it to an elevated temperature, quenching and reheating to an intermediate temperature at which full or complete precipitation occurs, that is further precipitation' cannot be effected by any further heat treatment alone. when precipitation hardened this alloy is relatively soft. I have found however that its properties may be improved by state may be double aged by the application of sufllcient strain to the precipitation hardened alloy and by reheating for a sufllcient length of time at temperatures below those eflecting any recrystallization in the alloy.

I have found that double ageing may be eifected in precipitation hardenable alloys'by one of the following processes:

-(a) Precipitation hardened, thermally strained then given a second ageing treatment.

5 (11) Precipitation hardened, cold worked, then given a second ageing treatment.

' (c) No solution treatment, first ageing; then applying a thermal strain and finally giving a second aging treatment.

,(d) No solution treatment, first ageing, cold working, then giving a second ageing treatment.

2 Process (a) may be applied to certain aluminum base'allcys, for example alloys of .the following type This process may also be applied to advantage to certain copper base alloys, for example 5 Ni5 Sn--0.2 to 2% Zn88 Cu 7.5 Ni-B Sn0.2 to 2% Zn82.5 Cu

Process (0) as set forth in my copending application Serial No. 247,488, filed December 23, 1938 may be applied to advantage to the following aluminum base alloys: V

Process (d) ma be applied to aluminum base alloys ofwhich the following is an example:

5 on Si-1.3 Mg0.25 Cr97.75 A1 The expression thermal strain" as employed in the present specification and claims means a strain obtained by a controlled cooling from the 40 first precipitation reheat, for example cooling at a rate to induce a condition of critical strain in the alloy, that is, water or oil quenching, or rapid air cooling.

The present invention is concerned principally 5 with those alloys to which process (b) is par- The copper base alloys, to

ticularly applicable. which the present invention is directed, are mechanically strained by cold working, for example by producing a permanent change in dimension of the metal or alloy by mechanical means operating on the metal or alloy while they are at temperatures below that of recrystallization for the particular metal or alloy. Cold working to pro duce a uniform or regular change in dimension may be accomplished by swaging, forging, rolling, drawing or extruding. Cold working to produce localized change in dimensions may be accomplished by cold shaping or by a cold failure of the metal or alloy due to tension, compression, torsion or frictional-wear.

In accordance with prior art precipitation hardening processes, if a cast rod about 1% inches thick and consisting for example of .4% chromium, 0.1% beryllium and about 99.5% copper is precipitation hardened by heating for about one hour at 900 C., quenching .in cold water, cold swaging to about one inch diameter and then reheating at about 475 C. foran hour,

the following properties are obtained:

- Tensile strength pounds per sq. inch- 47,700 Proportional limit do 30,000 Elongation -1 per cent--. 27 Eardness Rockwell B 63 Electrical conductivityuper cent that of copper 71 hour at a temperature of about 900 0., quenched in water, reheated at about 500 C. for one hour.

air cooled and then mechanically strained .by swaging to effect a reduction in diameter of about 50% the following properties'are obtained:

Tensile strength pounds per sq. inch 50,000 Proportional limit do 40,000 Elongation "per cen 13 Hardness Rockwell 13-- 72 Electrical conductivity per cent that of copper..- 67-70 The production of a mechanical strain in the alloy by cold working after precipitation hardening effects a marked increase in tensile strength. proportional limit and hardnessand the resulting product is characterized by the comparative freedom from slip bands ordinarily present in cold worked material. The production of a. mechanical strain in the alloy may of course be produced by anyof the means hereinbefore set forth. If the precipitation hardenedaod is new maintained or reheated at a temperature of about 100 C. for about 1 /2 hours and air cooled the following properties are obtained in the double aged alloy:

Tensile strength pounds per sq.

inch-.. 65000-704100 Proportional limit do 43,000 Elongation per cent-.. 9-12 Hardness Rockwell 13-- 74-78 Electrical conductivity per cent that of copper 66-70 The present process of double aging is not limited to the use of a second aging temperature of about 100 C. Ifthe particular copper-chromium-beryllium alloy herein disclosed is pre cipitation hardened in accordance with prior art practice and thereafter cold worked to effect a desired condition of strain, for example by a cold reduction of about or it may be aged thereafter at any temperature from about C. to 500 C. without loss in hardness or change in its micro structure even. when subjected to a stress of 5000 pounds persquare inch at 500 C. for 4000 hours. Aging in this range results in an increase in elongation up to 20% and an increase in electrical conductivity up to 75% without changes in other properties as noted.

The maximum upper temperature which may be employed in the second, aging step may be determined readily by trial heating at various temperatures. Ordinarily, there is no change in hardness up to the temperature of the first precipitation hardening step. A sharp decline in hardness of the alloy, obtained by heating the alloy at some temperature abov the temperature of the first precipitation hardening step, indicates that recrystallization has taken place in the alloy. In the copper-chrome-beryllium alloy a decline in hardness is obtained at a temperature of about 525 C. indicating the beginning of recrystallization at this temperature. The maximum service temperature for double aged copper base alloys treated in accordance with the present process is substantially the critical precipitation temperature, for example in the copper-chrome-beryllium alloy disclosed herein, about 500 C.

I haveillustrated my invention in connection with copper-chrome-beryllium alloys, but, as hereinbefore set forth, it is not limited to such alloys and may be applied to any copper base precipitation hardenable alloy. However, the improvement which may be obtained in some of these alloys may not be of such a degree as to warrant the added cost of the present treatment.

The following is a partial list of alloys which, when subjected to the double aging process hereinbefore disclosed all show improvement in physical properties over those obtained by means of a simple precipitation hardening process. This list is not complete but merely representative. Also, it will be understood that the present process is not limited to alloys which have the exact percentages of ingredients recited in these examples.

1. 0.9% Cr, remainder Cu. 2. 0.9% Cr, 1% Co, remainder Cu. 3. 3.5% Fe, 3.6% Co, remainder Cu. 4. 2.3% Ag, 1.2% Co, remainder Cu. 5. 2.5% Cd, 1.2% Co, remainder Cu. 6. 3.5% Fe, 7.2% Co, remainder Cu. '7. 2.5% Cd, 2.5% Co, remainder Cu. 8. 0.1% Be, 0.4% Cr, remainder Cu. 9. 0.1% to 3% Sn, 0.1% to 3% Co, remainder Cu. 10. 0.2% to 5% Fe, 0.2% to 7.0% Co, remainder Cu. 11. 3.5% Fe, remainder Cu. 12. 2.3% Ag, remainder Cu. 13. 4.6% Ti, remainder Cu. 14. 1% Ti, 1.2% Co, remainder Cu. 15. 10% Al, remainder Cu. 16. 0.2% to 3% Zr, remainder Cu. 17. 3% Zr, 2% Co, remainder Cu.

Double aged precipitation hardenable alloys in general yield the unusual combination of high values in elastic limit, proportional limit, elonga- 'tion, electrical conductivity, resistance to shock 2,275,188 R J .n 3 I ,Thus, double aging eflects a useful increase in the service temperature and resultsin greater stability of useful properties; What I claim as new and desire to secure by Letters Patent of the United States, is:

v L'The process for improving'the properties,

of a precipitation hardenable alloyconsisting of 0.2% to 3% zirconium with the remainder copper which comprises fully precipitation hardening said alloy, superimposing a condition of strain.

upon the precipitation hardened alloy and thereafter aging the alloy at a temperature below that V which affects any recrystallization in the alloy and below the temperature employed lnpreciDitation hardening said alloy.

2. The process for improving the properties of j an. alloy consisting of 0.2 to 3% zirconium with the remainder substantially all copper which comprisesfully precipitation hardening said alloy, cold working the alloy and thereafter aging the alloy at a temperature below the temperature employed in precipitation hardening said alloy.

RIC ARDS H.- HARRINGTON; 

